The present invention is directed to an overload safety clutch, especially for use in manually operated drilling tools, where the torque transmitted from a drive side to a driven side is effected by a connection provided by a prestressed or preloaded spring element.
When using drilling tools, such as a drilling machine, a hammer drill, and diamond tip drilling tools, a large torque can be caused by the material being drilled. The maximum allowed torque for a tool of the type mentioned can be defined relatively accurately. The effect of the torque on the tool and especially in manual tools on the operator can be very different. If the operator stands on a ladder and operates the tool with only one hand, then he produces less opposing moment than if he is standing on the ground and applies pressure with his entire body against the drilling tool. In a hard material being drilled, the torque evidently increases more slowly than in the case when "hitting iron". In unfavorable applications and stability situations a very slight torque change, a reaction moment can result in accidents having severe consequences.
To protect against excessive torque, it has been known to use friction or ratchet clutches representing a compromise between operator and tool protection. However, the result of such compromise, is unsatisfactory, since known overload clutches, if the full output range of the tool is used, can result in accidents, as mentioned above, in view of the reaction moment developed in the drilling tool in the event the drill bit is seized.
To identify the malfunction based on the seizing of the tool bit and to trigger countermeasures in good time, for instance, by interrupting the drive train of the tool with a tool bit by a quick-acting electromagnetic clutch, various solutions have been known to avoid the problem before the operator is injured. As a rule, in electromechanical or mechanolelectronic solutions, where an acceleration component at the tool housing exceeding a predetermined threshold or a velocity component is determined on the basis of the reaction moment by means of a sensor responding to mass effects, such an indication is converted into an electrical signal and used for actuating or releasing the separation clutch. Examples of electromagnetic solutions employing velocity sensors are described in DE 33 46 215 A1 and WO-DE 88-00 109 and/or proposed in a modern solution using acceleration sensors and digital electronics in DE patent application P 43 44 817.8. In these electromechanical or mechanoelectronic solutions, a sensing system checks certain conditions, for instance, the rotational acceleration, a rapidly rising current value, a rising torque and the like. The electronics recognizes the malfunction as soon as the sensor signals excessive specific limit or threshold values and/or because of previously stored process development or operating conditions. The electronics then averts the dangerous consequences of the malfunction by suitable measures, such as uncoupling or braking the drive motor.
All of the known or proposed solutions require, apart from the sensor system, an electronic recognition processing and amplification circuit.